COLLECTIVE AND NONCOLLECTIVE MULTIPHONON STATES IN EVEN-EVEN SPHERICAL NUCLEI

The multiphonon method previously developed for even-even spherical nu clei used pairs of fermions as building blocks. The present extension is based on collective and/or non-collective phonons. Calculation of m atrix elements of one- and two-body operators between multiphonon stat es can be reduced to the determination of overlap matrix elements of s tates containing phonons and some pseudo-phonons General recursion for mulae for the evaluation of such elements are given and allow for nume rical calculations in a space spanned by a reasonably large number (n = 5-6) of realistic phonons.